1. Technical Field
The present invention relates to implantable cardiac devices. More particularly, the present invention relates to the collection, storage, transmission, processing, and presentation of information provided by an implantable cardiac device.
2. Description of the Prior Art
Implantable cardiac devices, such as pacemakers and defibrillators, have evolved into sophisticated data processing systems that continuously monitor a patient's cardiac activity and apply corrective, often life saving, therapy to the patient's heart in response to detected irregularities in such cardiac activity.
In addition to providing cardiac therapy, known devices are capable of providing a limited amount of information relating to device status and activity at the time of detected cardiac arrhythmias for review by an attending physician or other clinical personnel. Such information is usually accessed through the use of telemetric techniques, i.e. through the use of two-way communications between the implanted device and an external instrument for monitoring and programming of the implanted device and displaying telemetered information from the implanted device. During such telemetric communication, the device is interrogated by the external instrument, and status and other information stored by the device is then communicated to the external instrument.
It is known to monitor the operation of a pacemaker and provide electrocardiogram and associated pacemaker diagnostic information. This approach monitors real time cardiac activity such as patient electrocardiogram (`ECG`) and pacemaker recent history such as number of paced events, and number of corrective pulses applied by the device. Such device is useful for patient cardiac monitoring, for example in a physician's office or hospital, but unfortunately does not provide insight into cardiac activity and corrective action taken or not taken by the device apart from such real time monitoring. That is, if the sensed or paced events are not observed by the physician during such real time monitoring, it is not possible to determine with a high degree of precision and accuracy what particular therapy the device provided.
In E. Duffin, The Marker Channel: A telemetric Diagnostic Aid, PACE, vol. 7, pages 1165-1169 (November-December 1984) an approach to cardiac monitoring is discussed in which a pacemaker is monitored by telemetric techniques at the same time that a patient's ECG is taken. A printout is generated that plots the ECG information obtained with time-correlated pace therapy information. This information is indicated by specifically encoded signals that are output by the pacemaker.
Although plotting pacemaker activity against ECG data is of some use in diagnosing pacemaker failure and/or functionality or for observing cardiac events in real time, the type of information provided is limited to actual cardiac events that are viewed as they are occurring. Thus, such information does not provide any insight into long term cardiac activity and patient response to corrective therapy applied by the device.
It is also known to monitor a patient's ECG to provide a record of the event that triggers the application of corrective action by the device, as well as the specific action taken by the device, and patient response thereto. Such information is stored for later review and analysis, for example by a physician during a patient visit to the physician's office or at a hospital. See, R. Fischell, Recorder With Patient Alarm and Service Request Systems Suitable for Use With Automatic Implantable Defibrillator, U.S. Pat. No. 4,295,474 (20 Oct. 1981) in which a defibrillator stores ECG data with regard to cardiac state immediately before and after the triggering cardiac event. The total number of corrective pulses applied by the device and the total number of fibrillation events are also counted. Such stored activity totals may be output from a simple device memory as well as various housekeeping data that are formatted within a data frame that may also include pre- and post-cardiac event patient ECG data.
However, it is not possible to determine accurately or precisely why the device took the action it did. It is therefore not possible to determine if the device is functioning in an optimal manner or if the device is applying the most appropriate therapy for the arrhythmic episode. Nor does the device indicate in useful detail what specific action was or was not taken by the device, e.g. the voltage of the corrective pulse(s) applied. Rather, the device merely stores a summary of device activity, i.e. the number of fibrillation events and number of corrective pulses applied. Thus, it is difficult for a physician to determine if the therapy should be modified, or if the therapy is being properly applied, e.g. if therapy is not being erroneously applied in response to detection of bigeminal rhythm, or if the voltage of the shock administered by the device is excessive.
Similar devices are also discussed in A. Langer, M. Mower, Arrhythmia Recorder For Use With An Implantable Defibrillator, U.S. Pat. No. 4,223,678 (23 Sep. 1980) which provides a defibrillator that may be operated to send ECG and other information to a separate remote recording device by means of telemetric communication; and in G. Fountain, D. Lee, D. Kitchin, Patient ECG Recording Control For An Automatic Implantable Defibrillator, U.S. Pat. No. 4,625,730 (2 Dec. 1986) where an alarm signal is generated upon detection of a triggering cardiac event and corresponding defibrillator operation. The alarm alerts the patient who may then operate a recording device and thereby store ECG information that is generated during the cardiac episode for later review by a physician.
The Cadence V100 implantable defibrillator manufactured by Ventritex, Inc. provides both stored and real-time ECGs. It also separately provides diagnostic information regarding the type of arrhythmia detected and responsive therapy applied by the device. The system does not, however, provide a time correlated output of the ECG and device diagnostics which would greatly improve the ability of a physician to analyze device operation and effectiveness.
In another group of state of the art devices, a marker channel is provided with real time ECGs. This channel provides coded markers which are indicative of device operation such as delivery of pacing pulses, sensing of VT, sensing of VF and defibrillation output pulse. While this is helpful information, it does not provide a clear indication of why a particular therapy was or was not applied. Additionally, various false triggering events and/or the successful avoidance of such events is not reported. For example, such devices are not capable of reporting the occurrence of bigeminal rhythm and its appropriate non-treatment.
Given the critical need to continually monitor the heart activity of a patient having a cardiac condition, particularly a patient who requires regular application of corrective heart stimulation, for example a patient who needs an implanted cardiac therapy device, and further, given the need to supervise the actual corrective therapy applied by the device to the patient's heart in response to detected triggering cardiac events, it would be useful to relate cardiac activity with device action throughout each arrhythmic episode, including precise information relating to patient ECG prior to the onset of the arrhythmic episode, the exact therapy applied by the device and the reason why therapy was or was not applied by the device, and the patient's response to such therapy.
It would therefore be an extremely valuable diagnostic measure to provide an actual, rather than approximate or abstract, record of each arrhythmic episode, including pre-episode activity, the arrhythmia diagnosis, therapy applied, and patient response to such therapy. It is also of critical importance that such information be presented in a format that is readily understood by an attending physician, without having the physician waste time in interpreting various unrelated abstracted data to try to approximate the meaning of the complex interplay of several interrelated actions during an arrhythmic episode.